September Solar Generation and Export Numbers
Here is the overview for September 2025. The three cheap rates times are still the same, 4am-7am, 1pm-4pm and 10pm until Midnight. The rate at those times is 12.756p per kWh. The price cap is 26.01p. There is a peak rate of 45.422p between 4pm and 7pm. All other times it is 26.012p. The batteries cover the two higher rates.
It felt like a poor solar month, bit looking back a previous years it was our 2nd best. In fact it was 70 kWh better than last year. We had multiple Free Electricity Sessions, a Saving Session, plus our quarterly wind farm dividend came in. The results of those can be seen below.
Bill showing Free Electricity Rewards and Wind Farm Dividends
This month we generated 403.30 kWh and exported 61.40 kWh. I count an exporting day as a day when we export more than 10p. We didn’t export on many consecutive days which points to the batteries not being fully charged. Our system will charge from the grid if the batteries does not reach 100% for 7 consecutive days. This led to us using 91 half hours slots. I had been suspending the battery from 4am to 7am at the start of the month, but with some poor solar days forecast, I decided to force charge at those times instead. We exported on 18 days.
This year we have had 180 days where we generated more solar than we consumed, and 96 days more solar was generated than we imported from the grid. In September, 9 days the solar generated more than we imported, and of those 25 days more than we consumed.
According to the Octo-Aid app this was the breakdown of our usage per rate.
Grid Usage by Rate (High, Mid and Low)
You can see the heat pump statistics here.
The worst generation day was the 17th with only 3.30 kWh. The last time solar generation was that low was February! The best was the 5th when 19.60 kWh was generated.
The best export day was the 2nd with 7.00 kWh.
As solar panels output declines over the years I have added the previous years generation to the table at the bottom. Of course weather comes into it as well, but I thought it would be interesting to track. I have added this post that shows each year as a graph.
Octopus Energy bill
Octopus Watch Tariff Comparison Report. This does not include exporting
Best Solar Generation
| Date | kWh | |
|---|---|---|
| Generation | 26th May 2023 | 32.90 |
| Front generation | 14th June 2023 | 19.80 |
| Back generation | 7th June 2023 | 14.70 |
| Worst generation | 12th December 2022 | 0.20 |
Solar Generation September 2025
| Date | kWh | |
|---|---|---|
| Best generation | 5th | 19.60 |
| Best front generation | 5th | 12.70 |
| Best back generation | 5th | 6.90 |
| Worst generation | 17th | 3.30 |
| Worst front generation | 17th | 1.70 |
| Worst back generation | 7th | 1.60 |
Best Solar Export and Profit
| Date | kWh | Profit | |
|---|---|---|---|
| Exported kWh | 15th June 2024 | 22.20 | |
| Exported profit | 15th June 2024 | 22.20 | £3.15 (15p kWh) |
| Profit day | 14th April 2024 | 18.20 | £2.67 |
Solar/Battery Export and Profit September 2025
| Date | kWh | Income/Cost | |
|---|---|---|---|
| Best kWh export - Battery & Solar | 22nd | 7.00 | |
| Best kWh export - Solar Only | 22nd | 7.00 | |
| Best export profit | 22nd | 7.00 | £1.05(15p kWh) |
| Cheapest Day | 8th | £0.18 |
The graph below shows the generation for both front and back panels
Total Solar Generation
The graph below shows generation, battery discharge, battery charging, export, import to use and consumption for 2025
Showing generation, battery discharge, battery charging, export, import to use and consumption for 2025
Generation
Overview for September
The graph below shows the generation for each day
Graph showing production for the month
The graphs below show the generation split between the front and back panels
Graph showing production for the front facing panels
Graph showing production for the back facing panels
The graphs below show the yearly generation split across both the back and front panels
Total Front Solar Generation
Total Back panel generation
Octopus Cosy
The costs shown here do include the standing charge. Any comparisons are compared to the unit cost if we were not on Cosy Octopus, which is 26.010p per kWh. The standing charge was 45.42p
September Grid Information
| Standard Tariff | 25.010p | ||
| Standing Charge | 45.42p | ||
| Cost from the grid | £ 33.34(Cosy) | £ 62.01(Standard) | |
| Savings including export | £37.88 | ||
| Exported | 61.40 kWh | £9.21 @ 15p kWh | |
| Charging slots used | 91 | ||
| Agile plunge slots used | 0 | ||
| Average unit slot price | 13.98p | ||
| Cheapest slot | 12.76p | ||
| Most expensive slot | 26.01p | ||
| House consumed | 552.30 kWh | ||
| Solar generated 2025/2024 | 403.30 kWh | 333.00 kWh | |
| Battery Charged/Discharged | 270.90 kWh | 261.40 kWh | |
| Percentage generated by solar | 73% | ||
| Self Sustained Days 2025 (More solar than consumed) | 180 | ||
| Self Sustained Days 2025 (More solar than we imported) | 96 | ||
Here is the Octopus Watch report summary
Octopus Watch summary
Featured posts
Solar panel performance declines over the years. I thought it might be interesting to see how mine compares. Of course weather comes into it, but hopefully this will be a useful guide.